The present invention relates to an image pick-up tube, and more particularly to the construction of the external target connection for a plurality of electrodes formed on the inner surface of the face-plate of the image pick-up tube.
In the conventional vidicons, a target consisting of a transparent thin film electrode or signal-plate electrode and an extremely thin film of photoconductive material such as Sb.sub.2 S.sub.3, Se,PbO or the like coated upon the transparent thin film electrode is formed upon the inner surface of the face-plate. The face-plate comprises a glass substrate and defines a light image incident window. Said face-plate is generally mounted on a vacuum glass tube through an annular ring made of a low-melting-point metal or alloy such as tin, indium or the like. The annular ring not only serves to seal the vacuum envelope in an air-tight manner, but also provides a target connection. The DC voltage is applied to the transparent thin film electrode on the face-plate through the target connection or signal electrode and the signal current is derived from the transparent thin-film electrode through the signal electrode.
In a color television camera using a vidicon, a plurality of transparent thin-film electrodes must be formed upon the inner surface of the face-plate in order to derive a plurality of different color video signals. Whereas in a camera for monochrome television, the annular metallic sealing ring serves as a signal electrode, as described above, in a color television camera the sealing ring must be divided into a plurality of segments which must be electrically isolated from each other so as to derive a plurality of color video signals. However, from the standpoint of maintaining a vacuum in the camera tube, the division of the annular sealing ring is not desirable. In order to overcome this problem in the conventional vidicons, metallic pins are placed in the vacuum envelope close to the target so as to provide the external connection for a plurality of transparent thin-film electrodes. However, this type of external connection increases the number of camera tube fabrication steps and associated defects because the metallic pins must be placed in the vacuum envelope and the electrical connection must be made between the electrodes on the face-plate and the metallic pins. The electric field near the target is thus adversely deformed because DC voltages are applied to the metallic external connection pins.
Furthermore, methods have been proposed for forming a field electrode in order to produce an optimum electrical field near the target, an electrode for preventing the secondary electron emission in the camera tube and an electrode for varying the potential applied to a localized area of the target. However, these methods have not been effectively employed in practice because of the difficulty of providing the external connection for these electrodes.
One of the objects of the present invention is to provide an improved external connection means for a plurality of thin-film electrodes formed on the inner surface of the face-plate of an image pick-up tube.
Another object of the present invention is to provide a color television camera with a single electron gun which has a target constructed to derive a plurality of different color video signals, and an external connection means for a plurality of thin-film electrodes on the target.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Pursuant to the present invention, a plurality of conductors are utilized for providing external connections for a plurality of thin-film electrodes disposed on the face-plate of an image pick-up tube. At least one of said plurality of conductors for external connection is in the form of a thin film which is electrically isolated from the other conductors by a thin insulating film. This thin insulating film serves to seal, in an air-tight manner, the vacuum envelope of the image pick-up tube together with the conductors for external connection extending from the thin-film electrodes formed on the inner surface of the face-plate to the outer surface thereof.
In another embodiment of the present invention at least one of the plurality of thin-film electrodes formed on the inner surface of the face-plate is a transparent thin-film electrode, and one pair of transparent thin-film electrodes are in the form of a comb which is arrayed in such a manner that the teeth of the pair of comb-shaped transparent thin-film electrodes are interleaved. A thin photoconductive film is coated on the transparent thin-film electrode so as to constitute a target. The photoconductive layer normally exhibits a high resistance so that a common continuous thin photoconductive layer may be formed all over the different transparent thin-film electrodes.
The electrodes formed upon the face-plate are not limited to the transparent electrodes, because some of them may be used to prevent secondary electron emission within the image pick-up tube, or to apply a predetermined voltage to a predetermined spot or localized area of the target thereby verying the spectral sensitivity.
The face-plate with the construction described may be mounted on a vacuum envelope made of insulating material through an annular sealing ring made of conductive material which is in contact with the thin insulating film. A conductive ring fitted over the vacuum envelope may serve as an external connection for one of the electrodes formed on the face-plate.
A plurality of transparent electrodes may be formed upon the inner surface of the face-plate in the form of multiple layers which are electrically isolated from each other by insulating layers or in a coplanar relation namely in monolayer so as to isolate all electrodes formed directly on the inner surface of the face-plate by adequate means. The comb-shaped transparent thin-film electrodes may be formed in a multilayer construction in such a manner that their teeth seem to cross each other when viewed in a direction normal to the face-plate.
The conductors used for the external connection of said plurality of thin-film electrodes formed on the inner surface of the face-plate are very simple so that the image pick-up tubes may be fabricated in a simple manner.